1. Field of the Invention
The present invention relates to a multilumen catheter and, in particular, to multilumen catheters designed to prevent ischemia in patients when the catheter is positioned within the body.
2. Description of the Related Art
It is often necessary to divert the flow of blood from a patient's blood vessel back to the same or a different blood vessel as part of treating a patient suffering from one or more of numerous health impairments, including cardiovascular disease, such as congestive heart failure. Although surgical cut-down procedures can achieve this, percutaneous insertion of catheters has made this procedure less invasive and therefore less traumatic to the patient. Still, insertion of a cannula into the circulatory system can cause complex, and sometimes adverse, reactions within the body.
Some of the percutaneous procedures involve removing blood from the body and subsequently returning it to the body. For example, dialysis treatment involves first removing blood from the patient's circulatory system, treating the blood outside of the body, and then returning the blood to the patient's circulatory system to perfuse the various tissues and organs. Depending on the volume of blood flow, cannulae with large carrying capacity may be necessary. By maximizing the cross-sectional area of the cannula, the volume of blood that may be removed and/or returned to the patient's vascular system via the cannula is maximized. One approach to maximize the cross-sectional area of the cannula involves using either two single lumen catheters or a multi-lumen catheter. In a recirculation application, one lumen would function to withdraw blood and one would function to return blood to the patient. One problem with using two single lumen catheters is that it subjects the patient to multiple percutaneous insertion procedures, which complicates the procedure and increases the potential for infection and other complications. Therefore, it would be desirable to have a catheter assembly which could be inserted into the patient through a single insertion site.
Multilumen catheters in various forms have been employed for this purpose. For example, multilumen catheters have been made with two, three or more lumens to serve various aspiration and infusion functions, including extracting and returning blood to vessels, taking blood samples for testing and providing medications to the patient's vascular system. Simple multilumen catheters have been made by providing two round catheters of equal or nearly equal length joined by a web, or thin strip. This approach is described in U.S. Pat. No. 5,776,111 to Tesio. Other multilumen catheter designs have a unitary body with at least one septum dividing the lumens which extend from a proximal to a distal end.
While multilumen catheters require only a single puncture of the epidermis, their performance is limited in at least two ways. For one, the outer perimeter of the multilumen catheter cannot exceed the inner diameter of the vessel into which it is inserted. Furthermore, the already limited cross-sectional area must be divided into at least two lumens, one for withdrawal and one for return. Thus the carrying capacity of each lumen is further reduced. To supply the same amount of blood, the velocity and pressure of the blood in the lumens must increase over what it would be in the vessel itself. This has the potential to cause damage to the vessel as blood comes jetting out of the return lumen. Also, it may put further stress upon blood cells, even causing hemolysis. Thus, multilumen catheters must be made as large as possible to carry enough blood at satisfactory conditions.
Where the size of a catheter approaches the interior size of a vessel, less and less blood can flow around the catheter. As a result, limited blood supply reaches tissues and organs located downstream of the catheter in the vascular system. With insufficient perfusion, the tissues downstream of the lumen insertion site suffer from ischemia and become oxygen deprived. Prolonged oxygen deprivation can lead to tissue damage, as is well known in the art. Therefore, it would be desirable to have a multilumen catheter that can maximize cross-sectional area of withdrawal and return lumens while at the same time providing for acceptable levels of blood perfusion of tissue downstream of the catheter insertion site in the vascular system. It would also be advantageous to have a multilumen catheter that can also remove blood from one peripheral vessel and return blood to a second peripheral vessel.